1. Field of the Invention
The present invention relates to a dual-band transceiver and in particular to a dual-band transceiver and its control method which are capable of performing transmission and reception operations in two different bands.
2. Description of Related Art
At present, there have been remarkably widely used mobile terminals in the mobile communication field, and there exist a plurality of systems with a large difference of frequency bands used. Under this circumstance, in order to improve the convenience for users, there has been a market demand that the users should be placed in a position to be able to utilize the plurality of systems with one set of terminal.
Various proposals have been made so far to meet such market demand. For example, Japanese Patent Application Laid-open Publication Nos. 5-244032 and 5-244033 disclose techniques in which two series of transmission systems and receiving systems are provided in a radio frequency stage, and frequency converters common to the two series of transmission systems and receiving systems are equipped with local oscillators respectively, thereby to make it possible to switch local frequencies generated by the local oscillators between a first frequency band and a second frequency band.
Further, Japanese Patent Application Laid-open Publication No. 10-84299 discloses a technique in which two series of transmission systems and receiving systems are provided respectively to make it possible to connect these systems to an antenna by switching between the systems.
On the other hand. Japanese Patent Application Laid-open Publication Nos. 61-131919 and 61-281627 disclose techniques in which a frequency converter for a transmission system and a receiving system is equipped with a shared single local oscillator, to make it possible to carry out a transmission and a receiving of signals in two different frequency bands with physically one circuit by utilizing a fundamental wave and a higher harmonic of the single local oscillator.
According to the techniques described in Japanese Patent Application Laid-open Publication Nos. 5-244032, 5-244033 and 10-84299, it is necessary to provide a plurality of transmitting and receiving circuits or a plurality of high-frequency local oscillators, and this becomes a big barrier in achieving a compact and light-weight terminal.
Further, according to the techniques disclosed in Japanese Patent Application Laid-open Publication Nos. 61-131919 and 61-281627, it is possible to make the terminal compact and light-weighted. However, since a fundamental frequency and its harmonics generated by the single high-frequency local oscillator are not used simultaneously and the frequencies are used in switchover, it needs a switching circuit and the complicated switching control thereof.
It is, therefore, an object of the present invention to provide a dual-band transceiver and a control method therefore, which make it possible to concurrently carry out a transmission operation and a receiving operation in two different bands with simplified circuit configuration.
Another object of the present invention to provide a dual-band transceiver and a control method therefore, which can achieve receiving and transmitting operations in a time-division fashion at one band while monitoring the signal strength at the other band.
According to a first aspect of the present invention, a dual-band transceiver operable in two different bands consisting of a first band and a second band, includes a local oscillator for generating a first local signal having a first frequency and a second signal having a second frequency which is a multiple of the first frequency; a receiving circuit for receiving a high-frequency signal in a selected one of the two different bands using the first local signal; a transmitting circuit for transmitting a high-frequency signal in a selected one of the two different bands using the second local signal; and a controller controlling the local oscillator and the receiving and transmitting circuits such that a transmitting operation in the first band is performed in a time period while a receiving operation in the second band is performed in the time period.
Since a single local oscillator is used to enable transmitting and receiving operations in the two different bands, a simplified circuit can be achieved. Further, since the receiving operation in the second band can be performed during the transmission operation in the first band, it is possible to monitor the propagation condition of the second band during communication in the first band.
According to a second aspect of the present invention, a dual-band transceiver includes: a local oscillator for generating a first local signal having a first frequency and a second signal having a second frequency which is a multiple of the first frequency, wherein the first frequency is variable; a receiving local oscillator for generating a receiving local signal having a variable receiving local frequency; a transmitting local oscillator for generating a transmitting local signal having a variable transmitting local frequency; a receiving circuit for receiving a high-frequency signal in a selected one of the two different bands using the first local signal and the receiving local signal; a transmitting circuit for transmitting a high-frequency signal in a selected one of the two different bands using the second local signal and the transmitting local signal; and a controller controlling the local oscillator the receiving and transmitting local oscillators, and the receiving and transmitting circuits such that a transmitting operation in the first band is performed in a time period while a receiving operation in the second band is performed in the time period.
The controller may control the local oscillator such that the first frequency is set to near the second band and the second frequency is set to near the first band and further control the receiving and transmitting local oscillators such that the variable receiving local frequency is set to enable the receiving operation in the second band and the variable transmitting local frequency is set to enable the transmitting operation in the first band.
Since an oscillator generating a relatively low frequency can be used as the receiving and transmitting local oscillators, a simplified circuit can be achieved. Since at least one of the receiving and transmitting local frequency is variable, the receiving and transmitting circuits is allowed to be highly adaptable to any dual-mode system.